I'm in Scotland, had my fresher's week a couple of weeks ago. I really enjoyed it. My uni - or rather, the union and all the societies - put on loads of events. I met most of my uni friends standing in line for a James Bond themed party 
You don't have to get totally hammered to enjoy yourself - being tipsy is often enough, or just being around other people who are more drunk than you are. As some people have said, being part of a group of people who are between moderately and extremely drunk tends to lead to fun times. I've only got really drunk once since starting uni, and it was honestly huge fun.
As for age, I'm only 17 and so not legally allowed to buy alcohol yet which I'd say is worse than being 20. I know a few people who are 20/21 and they've been fine - I don't think a few years difference really matter when you're all freshers.
You don't have to get totally hammered to enjoy yourself - being tipsy is often enough, or just being around other people who are more drunk than you are. As some people have said, being part of a group of people who are between moderately and extremely drunk tends to lead to fun times. I've only got really drunk once since starting uni, and it was honestly huge fun.
As for age, I'm only 17 and so not legally allowed to buy alcohol yet which I'd say is worse than being 20. I know a few people who are 20/21 and they've been fine - I don't think a few years difference really matter when you're all freshers.